Mr Thomspon went on radio this morning to debate gender inequality - it was largely uncontroversial until he tried to explain why women are paid, on average, 12 percent less than men.

"Look at who takes the most sick leave," said Mr Thompson. "Because you know, once a month they have sick problem. Not all women, but some do. They have children and they have to take leave off."

Mr Thompson says he didn't mean to upset anyone, that he's a supporter of equal pay for men and women and he's sorry.

"The first thing I want to do is apologise to any person, man or woman, because some men have taken offence too," he says.

"I am sorry that I have given offence."

He might be sorry, but he meant what he said.

"Women take more sick leave in general," he says. "I know it's an awful thing to say, but it's true."

3 News asks him again if this was true.

"Don't interrupt me, otherwise I will stop the interview," he replies.

The "monthly sickness" comments have caused outrage. Mr Thompson has received hate emails and the woman he was debating on air says he should resign.

"It's this sort of attitude that contributes to the pay gap," says Helen Kelly of the Council of Trade Unions, "and won't change with the people like Alasdair at the head of these organisations."

One of country's top lawyers says he was out of line.

"I like Alasdair Thompson," says Mai Chen. "I've known him a long time but he's got the facts wrong. I am a female employer, I have a child. Half of my staff here are women and a lot of them have children, and we are New Zealand's top public law firm."

Minister of Labour Kate Wilkinson says if Mr Thomspon worked for her, he'd be in for a telling off.

"I'm not responsible for his comments but I think he had a brain explosion," she says. "It's ridiculous, it's ludicrous."

"He sounded a bit like a dinosaur to me," says MP Paula Bennett.

"I think his comments are outrageous," says Greens leader Russel Norman. "He basically said women should be paid less because they menstruate, let's not gloss."

Statistics New Zealand doesn't have information about which gender takes the most sick leave, but Mr Thompson says he knows its women from his own experience and from the employers he represents – but he can't prove it.

"I can't because I haven't got the information on me.

3 News asks if he had any rough figures to back up his claims.

"I don't do roughly," says Mr Thompson.

He says he wasn't talking about all women or even a large proportion, because many control their "monthly sickness" with Panadol.

3 News asked if he truly believed the menstrual cycle was really big enough a problem it would impact on women's productivity.

After a loing pause, he said "cut" and the interview was over.

He might have given an apology, but Mr Thompson is adamant he's right.